The invention relates to ink-jet printers and, in particular, to surface modified nozzle plates for printheads which exhibit modified wettability characteristics.
Ink jet printer technology continues to improve to provide faster printers which produce higher quality print. In order to achieve these goals, printhead materials, designs and manufacturing procedures continue to change and evolve. In newer printhead designs, the nozzle plates contain smaller, more closely spaced nozzle holes and increased numbers of nozzle holes per nozzle plate. As the size and spacing of the nozzle holes decreases and the need for increased production increases, it becomes increasing difficult to provide relatively inexpensive printheads which function to provide quality print over the life of the printhead.
One of the problems which may occur during a printing operation is that ink accumulates on the nozzle plate surface adjacent the nozzle holes. Tile accumulated ink can, over time, partially block and cause misdirection of ink droplets ejected from the nozzle plate or, in a severe case, totally block ink ejection from the affected nozzle hole. An excess accumulation of ink on the nozzle plate adjacent a nozzle hole during firing of a nozzle is often referred to in the art as xe2x80x9cfloodingxe2x80x9d since the ink may actually accumulate to the point that it covers the nozzle holes. Another accumulation of ink on the nozzle plate is the result of ink pooling. xe2x80x9cPoolingxe2x80x9d is defined as the accumulation of ink on the nozzle plate when a xe2x80x9ctailxe2x80x9d of ink forms as the ink droplet is ejected and the ink tail breaks away from the main droplet and deposits back on the nozzle plate. Pooling of ink does not necessarily occur only adjacent the nozzle holes and may occur anywhere on the nozzle plate.
In addition to interfering with ink ejection from a printhead, ink accumulation on a nozzle plate of a multi-color printhead whether from flooding or pooling may result in ink color mixing. As a result of ink color mixing, the ink droplets ejected from affected nozzle holes may not provide the intended color dots thereby reducing print quality. As nozzle holes and their associated ink ejection heaters become smaller and the distance between adjacent nozzle holes is reduced to provide higher quality, faster printing, the effects of ink accumulation or flooding of the nozzle plates becomes a more important factor in the operation of the printer.
Attempts have been made to control nozzle flooding and pooling by applying certain fluorocarbon coatings to the nozzle plates. For example, U.S. Pat. No. 5,010,356 to Albinson describes a method for reducing the wettability of the surface of a substrate by providing an adherent layer of fluorosilane to an ink jet recording head. According to the method, a first layer of cured siloxane is formed on the surface and a second layer containing a fluorosilane group including a hydrolyzable group is applied to the first layer. The first siloxane layer is said to be cured (i.e., polymerized) on the surface by baking the coating at 50xc2x0 C. for thirty minutes, followed by baking at 45xc2x0 C. for thirty minutes and 95% relative humidity. The fluorosilane layer was said to be applied to the siloxane coated surface of the polyimide sheets in a dessicator which had a pressure of 50 torr pressure and a relative humidity of less than 10%. After applying the fluorosilane layer to the siloxane coated polyimide sheets, the dessicator was placed in an oven for 2 hours at 180xc2x0 C. After baking, the dessicator was cooled for 15 minutes, reconnected to a vacuum pump and evacuated while it continued to cool. The dessicator was then pressurized to room pressure using dry nitrogen gas. It was said that the non-wetting properties of the coated polyimide were still apparent after 1,000 strokes of a cotton bud soaked in tripropylene glycol monomethyl ether solvent.
Despite advances in the art of nozzle plate manufacture, the use of a siloxane layers and/or fluorosilane layers and conventional coating techniques to modify nozzle plate wettability have not been found to provide durable coatings for nozzle plates which remain effective over the life of the printheads which may include thousands of cleaning cycles. Conventional wettability modification coatings may be readily removed or rendered ineffective by techniques used to clean the printheads long before achieving the expected printhead life. Thus there remains a need for improved wettability modification coatings which are sufficiently durable to remain effective over the life of the printheads.
With regard to the above and other objects and advantages, tile invention provides an ink jet printer nozzle plate containing nozzle holes and having a durable non-wettable layer on at least one surface thereof. The surface heaving the non-wettable layer is positionable adjacent a media to be printed. The nozzle plate includes a polyimide material and the non-wettable layer contains a derivative of an amine-terminated silane compound, the amine-terminated silane compound derivative being covalently bound to the polyimide material of the nozzle plate. The layer also contains a derivative of a polydialkylsiloxane compound having a number average molecular weight ranging from about 400 to about 150,000 and an end group reactive with the amine-terminated silane compound derivative. The polydialkylsiloxane compound derivative is bound to the amine-terminated silane compound derivative by a condensation reaction to provide the durable non-wettable layer on the surface of the nozzle plate.
In another aspect, the invention provides a method for modifying surface wettability of a polymeric nozzle plate for an ink jet printer. According to the method, an amine-terminated silane compound is applied to at least a portion of a first surface of a nozzle plate made of polyimide material. The nozzle plate and the amine-terminated silane compound are heated for a period of time under conditions sufficient to covalently bond the amine-terminated silane compound to the polyimide material. Next, a polydialkylsiloxane compound is reacted with the covalently bound amine-terminated silane compound to provide a durable non-wettable layer on the first surface of the polyimide nozzle plate.
In yet another aspect, the invention provides a method for treating a first surface of a polyimide material to render the first surface substantially repellent to ink. The method includes applying an amine-terminated silane compound to a first surface of the polyimide material and heating the amine-terminated silane compound and polyimide material to a temperature sufficient to form covalent bonds between the amine-end groups and the polyimide material. A polydialkylsiloxane compound is applied to the covalently bound silane compound and the polyimide material containing the covalently bound silane compound and the polydialkylsiloxane compound are heated to a temperature sufficient to effect a condensation reaction between the covalently bound silane compound and the polydialkylsiloxane compound producing a durable non-wettable layer on the surface of the polyimide material. The durable non-wettable layer has a thickness ranging from about 0.5 to about 7 microns. The preferred polydialkylsiloxane compound has a number average molecular weight ranging from about 400 to about 140,000.
In an alternative embodiment, a mask is applied to the durable non-wettable layer on the nozzle plate to mask an annular area around the nozzle holes in the nozzle plate and certain unmasked areas are reactive ion etched (RIE) to increase their wettability. This provides areas on the nozzle plate which are wettable and areas which are non-wettable by the ink thereby improving excess ink removal during the printhead cleaning steps.
An advantage of the durable non-wettable layer and methods of the invention is that an effective non-wettable layer may be provided on a nozzle plate which has increased durability over the life of the printhead. Without desiring to be bound by theoretical considerations, it is believed the increased durability of the non-wettable layer is due, at least in part, to covalent bonds which are formed between the silane compound and the polyimide material of the nozzle plate as a result of the relatively high reaction temperature. Covalent bonds are formed when the polyimide and silane are heated to a temperature sufficient to open the ring structure of the polyimide so that a reactive end group on the silane can bond with the polyimide ring structure. The polydialkylsiloxane compound condensed to the silane compound derivative on the polyimide material further increases the durability of the coating by increasing the effective thickness of the non-wettable layer. Sixe2x80x94Oxe2x80x94Si bonds are formed between the silane and polydialkylsiloxane compounds at elevated temperatures due to the presence of reactive end groups oil the silane and/or polydialkylsiloxane compound. The resulting non-wettable layer is particularly resistant to damage or removal during printhead cleaning operations using a wiper as described herein.